This invention relates to a process for producing a nucleophile-substituted aromatic compound by iodizing an aromatic compound having an electron donating group by electrolytic oxidation reaction to obtain an iodized aromatic compound, and then allowing the iodized aromatic compound to react with a nucleophilic reagent. Particularly, the present invention pertains to a process which comprises obtaining p-iodoaniline (hereinafter abbreviated as PIA) from aniline (hereinafter abbreviated as AN) and then producing p-phenylenediamine (hereinafter abbreviated as PPD) therefrom.
PPD is useful as a synthetic intermediate for dyes, pigments, pharmaceuticals, monomers of aramide fibers, polyimide resins, etc.
A process for producing an aromatic compound by iodizing an aromatic compound with functional groups having an electron donating group by electrolytic oxidation reaction and then allowing the iodized aromatic compound to react with a nucleophilic reagent is disclosed in U.S. Pat. No. 3,975,439. In this patent it is disclosed that AN is iodized by an electrolytic oxidation reaction to obtain PIA, which is then allowed to react with ammonia. According to this process, PIA is obtained by electrolytic oxidation reaction by a diaphragm process, is allowed to react with ammonia and thereafter the ammonia iodide produced as a by-product is allowed to react with sodium hydroxide to recover ammonia and sodium iodide, the sodium iodide recovered being returned to the electrolytic system, to produce PPD.
When electrolytic reaction is carried out following the technique of the prior art, in the case of using a diaphragm, hydrogen iodide will be formed during the electrolytic reaction, whereby the electrolyte abruptly becomes acidic. The anolyte, which is initially a two-layer system of oil and water, will become a homogeneous system with the progress of electrolysis. Although there is no description of this, as a means for ensuring separation of the anolyte by the decanter, there is a description about maintaining the pH within the range of from 5 to 8 by addition of an aqueous sodium hydroxide solution.
However, as shown in the Comparative Examples of this application, when electrolytic reaction is carried out while adding an aqueous sodium hydroxide solution, it has been found that not only maintenance of pH within the range of from 5 to 8 is very difficult, but also the voltage will also change considerably, whereby it is very difficult to stably carry out the electrolytic reaction. Further, by-products such as azobenzene, 4-aminodiphenylamine, etc. are formed, although small in amounts. It is also observed that the oil layer has migrated through the diaphragm (in this case, Nafion membrane is used). On the other hand, also in using no diaphragm, current efficiency will be lowered to a great extent, and the by-products of azobenzene and 4-aminodiphenylamine are formed in large amounts.